A New Take on Warping Spacetime

by Paul Gilster on July 24, 2008

For those of you who don’t see Spaceflight, a magazine published by the British Interplanetary Society, it may be useful to know that an article by Richard Obousy and Gerald Cleaver (Baylor University) on warp drive theory from the April issue is now available on the arXiv server. This material was presented at the November, 2007 symposium held by the BIS in London. Kelvin Long, who organized the session, had earlier passed along several documents from the proceedings that we looked at here, and also wrote up the duo’s ideas in the same issue of Spaceflight.

But let’s backtrack a minute to Miguel Alcubierre’s 1994 paper, which demonstrated that it would be possible — within the context of General Relativity — to envision a space drive that could get you to your destination in a time shorter than it would take light itself to get there. Contracting space in front of the craft while inflating it behind, the drive is permissible because the starship itself would not be going faster than light. Rather, the space around it would be moving in such a way as to make the trip possible.

And that’s the key — the speed of light stricture does not apply to spacetime itself. Can we learn how to generate a region of expanding spacetime and one of contracting spacetime? Obousy and Cleaver argue that nature can offer insights, for spacetime itself is already expanding, a fact we realized with the work of Edwin Hubble in 1929 and have been wrestling with in various ways ever since. A warp drive would demand that the slow expansion of space that we observe be made to function extremely quickly, which makes understanding the cosmological constant the key demand of any attempt to build a true warp drive.

Now we’re truly in deep water, for attempts to explain the cosmological constant using quantum field theory have been shown to be off by a factor of 10120, an obvious marker of how far from descriptive current explanations are. The authors then turn to supersymmetry — the theory that all particles have an associated superparticle with a differing spin — to explore the question. And in rapid order they consider the cosmological constant in terms of higher dimensions, relating these first to the work of Theodore Kaluza, who suggested a fifth dimension in 1919, and then in ongoing efforts to explore extra dimensions using string theory.

Thus a potential scenario for an Alcubierre-style warp drive emerges:

In a recent paper, we addressed the plausibility of locally inﬂuencing the size of the extra dimension to locally (by local, we mean in the vicinity of a spacecraft) adjust the cosmological constant. This could theoretically create a modiﬁcation of spacetime around a craft that could be tuned to acquire the characteristics of the Alcubierre bubble… The basic idea is that by altering the radius of an extra dimension, it would be possible, in principle, to adjust the energy density of spacetime (which relates directly to the cosmological constant which ultimately controls the inﬂation/contraction of space itself). We have taken two approaches to this concept: one from the viewpoint of QFT another from GR. The equations of both theories indicated that the physics of the extra
dimensional space eﬀects the expansion rate of ‘normal’ space by a ‘dimensional shearing’ eﬀect. The equations of GR demonstrated that shrinking the extra dimension would inﬂate our space, and that expanding the extra dimension would contract our space. In this way, a bubble of expanding/contracting spacetime could be created at the rear/front of a spacecraft.

How fast might a warp-driven spacecraft go? Obousy and Cleaver work out an upper limit on such a velocity (based upon quantum field theory) of 1032c, c being the speed of light. Mind boggling to be sure, but tempered by the fact that the energy required for such a velocity is significantly greater than that available in the observable universe. Another of those ‘small problems of engineering,’ as Robert Forward used to call them…

Clearly, we’re up against huge hurdles, many of them suggested by this paper. Will we validate the idea of supersymmetry in the near future? Will some variant of string theory be subjected to experimental analysis, and if so, how? What sort of engineering would actually contribute to manipulating an extra dimension even if we were able to find one? No, I wouldn’t expect a warp drive breakthrough any time soon, but laying a theoretical basis for a technology has to be step one. That means parsing the issues and identifying potential solutions, some of which may be investigated and perhaps demonstrated in subsequent experiments.

Holy Moly, 10 EXP 32 C!. Perhaps if the craft can be accelerated down and inside of a superconducting tube of cosmic length dimensions, perhaps quantum field theory would permit velocities much much greater than 10 EXP 32 C. If the space craft can be rotated in a direction perpendicular to its direction of travel until the point where differential circumferential elements of the space craft tangent to the circumference of rotation are Lorentz contracted, perhaps the width of the space craft can be shrunk to that of a near point. The result, perhaps being the ability of the craft to travel down a superconducting tube of cosmic length wherein the tube would have a diameter or width on the order of 10 EXP -12 meters or less thus filtering out zero point electromagnetic fluctuations with half wavelengths of one pico-meter or less wherein the nodes of the filtered photons would fall on the inner surface of the tube.

Thus, the interaction of the space craft with the electromagnetic zero point fields in such a way that the zero point fluctuations would become real particles with real drag might be mitigated thus permitting terminal velocities many orders of magnitude greater than 10 EXP 32 C.

Now, the caveat is how to distort the space-time within the rotating craft such that it can rotate so quickly that its radius shrinks to microscopic dimensions.

But either way, when I saw the limiting value of 10 EXP 32 C, I instantly had renewed hope that we will somehow get to the stars, a hope that is sometimes tempted to discouragement by the lack of wide spread interest within the U.S. for manned space travel.

I certainly hope that we will go back to the moon by 2020, then onward to Mars, then onward to the Oort Cloud, and then to the stars and beyond.

I hope that when we first set boots on an extra solar terrestrial planet, the legacy of each and everyone of those who have held positions within the organization of Centauri Dreams and Tau Zero as well as all of us who contribute comments and continue the fine discussions here at Tau Zero will be remembered. But ultimately, even though we at Tau Zero right here and now are pioneers in the intellectualization and facilitation of manned interstellar travel, we work for a far greater cause, and that is of spreading humanity throughout the cosmos and that of meeting and sharing in fraternal charity, any of our ETI brothers and sisters, many of which I feel will congratulate us in a job well done when we finally land on an extra solar world.

Well this is the nub of the problem – it isn’t one of velocity but one of energy input. There is little utility in the Alcubierre type of drive unless the energy budget can, somehow, be made low. We already know how to travel arbitrarily fast in normal space – it, too, requires an enormous quantity of energy.

Any hope in the Alcubierre drive is if, in some currently unknown and perhaps impossible way, we can achieve the negative energy effect without utilizing a similar amount of positive energy. If we do have that much positive energy we can more readily employ it in a conventional (that is, non-warp) drive.

There is actually two different theoretical concepts for “warping” space. The first one is the original Alcubierre concept. Then there is the Inflation version of the same concept. The boys over at Earthtech (yes, I know I talk about them a lot) have several papers and presentations on this stuff. Thier conclusion is that at least the original version of the “warp” effect is not practical because of the huge amounts of energy required to create it and get significant speeds over C. However, they do conclude that, based on the theory alone, that the same effect can be used to make “wormholes”, which would be better anyways.

Speaking of unlimited energy reserves, I had the opportunity to visit the National Horticultural Society today with my mother and my brother John. A very impressive facility by the way! After seeing how a certain research program is studying how to grow food crops efficiently in modular pods, I started to think that if the energy released in the ATP reaction cycle within animal and human bodies could be amped up, perhaps the reaction pathway could be used to power ion rockets or other electrodynamic propulsion systems. I then realized that the reaction pathway results in at most about 9 kCal per gram of fat. Still, that is 9 times greater than the energy released in one gram of TNT at 1 kCal. This reaction pathway does not harm human or animal bodies because in animal life, the energy of food is released very slowly compared to the sudden energy release of TNT such as for mining and blasting or in artillery shells. Note that the energy released in a given mass of TNT is equal to the kinetic energy of an equal mass traveling at about 2.8 kilometers/second. A chemical propulsion system that was highly efficient using some sort of ATP reaction pathway might offer a good means for getting around the solar system especially if 3 or 4 stages where incorporated into a space craft.

I further begin to think that, “Man, if some sort of complex thermodynamic biological reaction sequence that involved some sort of catalysis by which the metabolic processes of ATP energy production could be renewed with recycled metabolic by products, where the energy yield of the ATP process was greater than the energy of recycling the metabolic by products, we might in essence have a perpetual energy creation system which could propel a space craft with free energy to ever higher gamma factors, provided some way of extracting and completely recycling drag induced by the CMBR, starlight, and baryonic matter was provided!” My thinking is that if there is any such free energy reaction pathways, they are probably most likely to be found in complex metabolic processes within animal life including the human body. Perhaps there just might be such an exotic pathway lurking within the midst of the huge number of thermodynamic degrees of freedom within the bodies of animals. If there is no such reaction sequence, perhaps animal metabolic sequences can some how be improved upon to provide any necessary complexity in order to probe for such free energy mechanisms.

I think the velocity 10^32 C is not possible, because the authors of the paper used the ADD theory which estimates that the extra-dimensions are a few micrometers and I really doubt about it. If we assume that the extra-dimensions are around 10^-18 m, then the velocity will reduce significantly. However, this velocity is still higher than the quantum hyperdrive from Ringworld universe.

Someone please recalculates the problem from the paper by R. Obousy and G. Cleaver, Warp Drive: A New Approach, arXiv:0712.1649 [gr-qc].

If something caused the energy release rate of ATP to accelerate like a chain-reaction that would neatly explain spontaneous human combustion – which still hasn’t been adequately explained, even by the much touted “wick effect” once promoted by sceptical investigators. The energy density though is about the same as kerosene which is already a good rocket fuel, but not spectacular.

I suspect that, like the many ‘credible’ ways to travel through time, all these theoretical confections will in reality be quite impractical. Yes, a bit of galactic engineering over a period of several billion years and with liberal quantities of Unobtanium-956 might allow a kilogram of mass to be seamlessly accelerated to, oh, 30 kph, but…

…let’s be reasonable.

We can send mass to the stars, slowly. Numerous studies show that this is an economic rather than a technical issue. And we can send information at lightspeed, and rather cheaply (if we care to).

I am new to the forum an I look forward to hopefully contributing to it. I’m no stranger to “FTL” and space warp concepts described on this forum, but I am in no way, shape, or form an expert. I do enjoy collaboration on advanced concepts and possibly coming up with feasible solutions. Thanks.

Michael, welcome, and have a look around via the archives and the search function. It’s a pleasure to have you join us. Do be sure to read the most recent statement about the Tau Zero Foundation — you can find it under the ‘Pages’ category on the main page.

Standard in almost every Star Trek episode are warp drives and cloaking devices. But in reality these science fiction gadgets defy the laws of physics. Or do they? Different scientists have been working on developing these two devices and they say they are getting closer to actually creating working prototypes. While warp drive won’t be available anytime soon, scientists are gaining a better understanding of how faster-than-light speed could possibly be achieved. And as for cloaking devices, don’t look now, but researchers recently cloaked three-dimensional objects using specially engineered materials that redirects light around objects.

Previously, scientists at the University of California, Berkley were only able to cloak very thin, two dimensional objects. But now, using meta-materials, which are mixtures of metal and circuit board materials such as ceramic, Teflon or fiber composite, scientists have deflected light waves around an object, like water flowing around a smooth rock in a stream. Objects are visible because they scatter the light that strikes them, reflecting some of it back to the eye. But the meta-materials would ward off light, radar or other waves. In effect, it would be a type of optical camouflage.

Include quantum mechanics in the calculations and faster-than-light drives become unstable

Friday, April 03, 2009

Bad news I’m afraid — it looks as if faster-than-light travel isn’t possible after all. That’s the conclusion of a new study into how warp drives would behave when quantum mechanics is taken into account.

“Warp drives would become rapidly unstable once superluminal speeds are reached,” say Stefano Finazzi at the International School for Advanced Studies in Trieste, Italy, and a couple of friends.

Warp drives have been the focus of science fiction writers for decades. But scientists kept them at arms length until 1994 when the idea was put on a firm (ish) theoretical footing by the Mexican physicist, Michael Alcubierre. His thinking is that while relativity prevents faster-than-light travel relative to the fabric of space time, it places no restriction on the speed at which regions of spacetime may move relative to each other.

Alcubierre imagined a small volume of flat spacetime in which a spacecraft might sit, surrounded by a highly distorted bubble of spacetime which shrinks in the direction of travel, bringing your destination nearer, and stretches behind you. He showed that this shrinking and stretching could enable the bubble–and the spaceship it contained–to move at superluminal speeds.

The conclusion is the result of classical thinking using the ideas of general relativity but physicists have long wondered what would happen if you threw quantum mechanics into the mix? Now Finazzi and pals have worked it. For a start, they say that the inside of the bubble would be filled with Hawking radiation, making life rather uncomfortable for any spacecraft within it.

They have also studied a property of a quantum field called the renormalised stress-energy tensor which should be well-behaved under normal circumstances. But in the front wall of Alcubierre’s bubble travelling at superluminal speeds, the renormalised stress-energy tensor grows exponentially.

That strongly implies that such a bubble would be unstable. So it looks increasingly likely that, after a brief few years of excitement, Alcubierre’s warp drive is impossible.

Here’s an idea: A scientific/technical contest to compose a metric with reasonably economical energy requirements for an Alcubierre-style “warp drive”. Specifically, what I’m suggesting is a prize for a “usable” warp bubble geometry solution. The prize would be, say, a billion euros. Or less… Right now I can kick in about 20 euros. Who’s with me?

Charter

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last nine years, this site has coordinated its efforts with the Tau Zero Foundation, and now serves as the Foundation's news forum. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

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